This issue looks similar to Bug ID -- 751376.
@mcnee -- Could you please look into the issue, kindly re-assign if this is not related to your changes.
Thank You.

ClusterFuzz has detected this issue as fixed in range 494497:494575.

Detailed report: https://clusterfuzz.com/testcase?key=5410429185818624

Fuzzer: ipc_fuzzer_gen
Job Type: windows_asan_chrome_ipc
Platform Id: windows

Crash Type: Null-dereference READ
Crash Address: 0x00000028
Crash State:
  guest_view::GuestViewManager::CanEmbedderAccessInstanceID
  guest_view::GuestViewManager::CanEmbedderAccessInstanceIDMaybeKill
  guest_view::GuestViewManager::GetGuestByInstanceIDSafely
  
Sanitizer: address (ASAN)

Regressed: https://clusterfuzz.com/revisions?job=windows_asan_chrome_ipc&range=491035:491089
Fixed: https://clusterfuzz.com/revisions?job=windows_asan_chrome_ipc&range=494497:494575

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=5410429185818624

See https://github.com/google/clusterfuzz-tools for more information.

If you suspect that the result above is incorrect, try re-doing that job on the test case report page.